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• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F110/00—Homopolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
  • C08F110/02—Ethene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/14—Peroxides
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
  • C08L23/06—Polyethene
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D123/00—Coating compositions based on homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Coating compositions based on derivatives of such polymers
  • C09D123/26—Coating compositions based on homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Coating compositions based on derivatives of such polymers modified by chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2500/00—Characteristics or properties of obtained polyolefins; Use thereof
  • C08F2500/08—Low density, i.e. < 0.91 g/cm3
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2500/00—Characteristics or properties of obtained polyolefins; Use thereof
  • C08F2500/12—Melt flow index or melt flow ratio
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2810/00—Chemical modification of a polymer
  • C08F2810/10—Chemical modification of a polymer including a reactive processing step which leads, inter alia, to morphological and/or rheological modifications, e.g. visbreaking
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2810/00—Chemical modification of a polymer
  • C08F2810/20—Chemical modification of a polymer leading to a crosslinking, either explicitly or inherently
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
  • C08J2323/26—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers modified by chemical after-treatment

Definitions

• the present invention relates to a process for the modification of low density polyethylene (LDPE) by reactive extrusion.
• LDPE low density polyethylene
• US 2010/0076160 discloses the reactive extrusion of so-called ‘tubular LDPE’ to increase the long chain branching index.
• LDPE is polyethylene having a density in the range 0.910-0.940 g/cm3 and is obtained by free radical polymerization of ethylene under high pressure. This process is either performed in an autoclave or in a tubular reactor. LDPE made by the autoclave reactor process (‘autoclave LDPE’) has a higher branching number than LDPE made by the tubular reactor process (‘tubular LDPE’). As a result, autoclave LDPE has a higher melt strength and is easier to process.
• melt strength of autoclave LDPE with MFI>4 g/10 min is generally 8.0 cN or more; whereas the melt strength of tubular LDPE with the same MFI is generally less than 8 cN. Melt strengths below 8 cN generally lead to inhomogeneous film thickness of the coating (high neck-in and poor draw-down).
• films obtained from reactively extruded LDPE tend to contain inhomogeneities, so-called gels. These are visual defects that transmit light differently from the rest of the material.
• gels consist of ultra high molecular weight polyethylene, formed by crosslinking. Gel formation leads to unacceptable aesthetic properties and to problems in printing and lamination processes; such as tearing of the film.
• LDPE cast film on cardboard used to improve the barrier properties of e.g. drink packages—may suffer from film tearing at large gel-particles (typically above 600 ⁇ m).
• the present invention therefore relates to a process for obtaining polyethylene with an MFI (190° C./2.16 kg) of at least 4 g/10 min and a melt strength (190° C.) of at least 8.0 cN, said process involving extrusion of low density polyethylene (LDPE) with an MFI of at least 5 g/10 min and a vinyl content of less than 0.25 terminal vinyl groups per 1000 C-atoms (measured with NMR in deuterated tetrachloroethane solution) with 500-5,000 ppm, based on the weight of polyethylene, of an organic peroxide.
• LDPE low density polyethylene
• Low density polyethylene is polyethylene having a density in the range 0.910-0.940 g/cm3 and being obtained by free radical polymerization of ethylene under high pressure.
• said LDPE may be obtained by using up to 10 wt %, preferably 0-7 wt %, and most preferably 0-5 wt % (based on the total amount of monomers) of co-monomers.
• co-monomers examples include vinyl acetate, vinyl alcohol, acrylates, methacrylates, butyl acrylate, ethyl acrylate, acrylic acid, methacrylic acid, and C3-C10 ⁇ -olefins, such as propylene, 1-butene, 1-hexene, and 1-octene.
• the LDPE to be modified according to the process of the present invention contains less than 0.25, preferably less than 0.20, more preferably less than 0.15, even more preferably less than 0.10, and most preferably not more than 0.08 terminal vinyl groups per 1000 C-atoms, as measured with NMR in deuterated tetrachloroethane (1,1,2,2-tetrachloroethane-d2) solution.
• the types of unsaturation that can be present in polyethylene are terminal vinyl groups (R—CH ⁇ CH2), vinylidene groups (RR′C ⁇ CH2), and cis- and trans-vinylene groups (RCH ⁇ CHR').
• the terminal vinyl content can be determined by 1H-NMR as described in the experimental section below.
• LDPE with such low vinyl content is generally not directly obtained from an ethylene polymerization process. Instead, LDPE has to be subjected to a special treatment, such as hydrogenation or hydroformylation (as described is WO 2014/143507), in order to reduce the vinyl content.
• a special treatment such as hydrogenation or hydroformylation (as described is WO 2014/143507), in order to reduce the vinyl content.
• the LDPE is extruded at a maximum temperature T, with a residence time tr, and in the presence of an organic peroxide with half-life t1 ⁇ 2 at temperature T (measured in monochlorobenzene), wherein tr/t1 ⁇ 2 ⁇ 400.
• temperature T The maximum temperature during the extrusion is temperature T. If the extruder contains multiple zones with different temperatures, temperature T corresponds to the highest temperature that is applied.
• Maximum temperature T preferably ranges from the melting temperature of the LDPE to be modified up to 240° C., more preferably 180-220° C., even more preferably 190-220° C., most preferably 190-200° C.
• the residence time in the extruder is defined as 1.5 times the BreakThrough Time (BTT), which is determined by introducing a pigmented granule(s) in the mouth of the extruder and measuring the time required for a pigmented polymer melt to leave the extruder die.
• BTT BreakThrough Time
• the residence time is preferably in the range 0.5-2 minutes.
• the ratio of the residence time and the peroxide's half-life at temperature T (tr/t1 ⁇ 2) is preferably less than 350, more preferably less than 300, even more preferably less than 250, even more preferably less than 200, even more preferably less than 150, and most preferably less than 100.
• the ratio of the residence time and the peroxide's half-life at temperature T is preferably more than 1, more preferably at least 5, even more preferably at least 10, and most preferably at least 15. Lower ratios may lead to residual peroxide in the polyethylene.
• the half-life of the organic peroxide is determined by differential scanning calorimetry-thermal activity monitoring (DSC-TAM) of a 0.1 M solution of the initiator in monochlorobenzene, as is well known in the art.
• DSC-TAM differential scanning calorimetry-thermal activity monitoring
• Preferred organic peroxides are monoperoxy carbonates and peroxy ketals with a 1 hour half-life—measured with DSC-TAM as 0.1 M solution in monochlorobenzene—of 125° C. or below.
• Particularly preferred peroxides include: 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,2-di(tert-butylperoxy)butane, 1,1-di(tert-butylperoxy)cyclohexane, 1,1-di(tert-amylperoxy)cyclohexane, butyl-4,4-di(tert-butylperoxy)valerate, tert-butylperoxy 2-ethylhexyl carbonate, tert-amylperoxy-2-ethylhexyl carbonate, and tert-butylperoxy isopropyl carbonate.
• the LDPE to be modified by the process of the present invention is tubular LDPE.
• Tubular LDPE is polyethylene made by free radical polymerization in a high pressure tubular process.
• the process according to the invention can modify said tubular LDPE into an LDPE with the quality of autoclave LDPE or even better (in terms of melt strength).
• the LDPE to be modified has a density within the range of 0.915 g/cm3 to 0.935 g/cm3, more preferably 0.918 g/cm3 to 0.932 g/cm3.
• the density can be measured according to ISO 1183/A.
• the LDPE to be modified has a melt flow index (MFI)—measured at 190° C. and with a load of 2.16 kg—of at least 5 g/10 minutes, preferably 5-100 g/10 minutes, more preferably 5-60 g/10 minutes, even more preferably 8-60 g/10 minutes, even more preferably 10-60 g/10 minutes, and most preferably 10-40 g/10 minutes.
• MFI melt flow index
• the LDPE to be modified preferably has a weight average molecular weight (Mw) of at least 100,000 g/mole. Such molecular weights are preferred for obtaining the desired melt strength. Mw can be determined with High Temperature Size Exclusion Chromatography (HT-SEC) as described in the experimental section below.
• Mw weight average molecular weight
• the organic peroxide can be added to the molten LDPE in the extruder, e.g. by liquid peroxide injection or by side feeding of peroxide blended in (LD)PE using a side extruder.
• solid LDPE e.g. pellets, powder, or chopped materials
• the peroxide may be separately added to the hopper of the extruder by spraying or dripping the liquid peroxide or liquid peroxide formulation on the polyethylene.
• the organic peroxide can be introduced as such, incorporated in an (LDPE) masterbatch or on a solid inorganic carrier (e.g. silica or kaolin), or dissolved or diluted in a phlegmatizer.
• Suitable phlegmatizers include linear and branched hydrocarbon solvents, such as isododecane, tetradecane, tridecane, Exxsol® D80, Exxsol® D100, Exxsol® D 100S, Soltrol® 145, Soltrol® 170, Varsol® 80, Varsol® 110, Shellsol® D100, Shellsol® D70, Halpasol® i 235/265, Isopar® M, Isopar® L, Isopar® H, Spirdane® D60, and Exxsol D60.
• the organic peroxide can be even further diluted with a solvent.
• suitable solvents include the phlegmatizers listed above, or other common solvents, like toluene, pentane, acetone or isopropanol.
• the organic peroxide is used in an amount within the range 500-5,000 ppm, more preferably 600-4,000 ppm, even more preferably 700-3,000 ppm, and most preferably 700-2,500 ppm, based on LDPE weight and calculated as neat peroxide.
• Amounts significantly higher than 5,000 ppm may result in crosslinked polyethylene instead of long chain branched polyethylene.
• Crosslinking (gel formation) is evidently undesired.
• the reaction of the polyethylene with the organic peroxide is preferably performed under inert (e.g. nitrogen) atmosphere.
• the reaction is preferably performed in the absence of additional compounds containing unsaturations, as their presence would increase gel formation.
• the modified polyethylene resulting from the process of the present invention has an MFI of at least 4 g/10 minutes, preferably in the range 4-15 g/10 minutes, and a melt strength of at least 8 cN.
• This modified polyethylene has many applications. It can be used in extruded films, including blown films and cast films. It can also be foamed and/or thermoformed. The modified polyethylene can also be used in molding, including blow molding.
• the polyethylene sample 50 mg of the polyethylene sample (powder or chopped material) together with 1 ml 1,1,2,2-tetrachloroethane-d2 (TCE-d2) were transferred into a 5 mm NMR tube.
• the NMR tube was purged with nitrogen gas and closed. The tube was placed in an oven at 120° C. to dissolve the polyethylene. After obtaining a clear transparent solution, the NMR tube was placed in the NMR spectrometer (Bruker Avance-IIIHD NMR spectrometer with a proton resonance frequency of 400 MHz using a 5 mm BBFOplus-probe).
• the content of the unsaturated groups was calculated as the fraction of the unsaturated group with respect to the total number of carbons present.
• the total amount of carbon was calculated from the bulk aliphatic integral between 2.80 and 0.50 ppm, accounting for the number of reporting nuclei and compensating for sites relating to unsaturation not included in this region.
• Ctotal (1/2)*(Ialiphatic+Nvinylidene+Nvinyl+Ncis/trans)
• LDPE Low density polyethylene
• Table 3 presents the different temperature profiles used for the experiments on the PTW16 extruder.
• the extruded strand was led through a water bath for cooling and granulated by an automatic granulator.
• the obtained granules were dried overnight in a circulation oven at 50° C.
• Cast film was prepared by extruding the obtained granules on a Dr. Collin Teach-Line E20T single-screw extruder, fitted with a Dr. Collin Teach-Line CR144T and CCD (Charged Coupled Device) camera for cast film preparation and gel evaluation. The following settings were used:
• the melt flow index (MFI) was measured with a Goettfert Melt Indexer MI-3 according to ISO 1133 (190° C./2.16 kg load). The MFI is expressed in g/10 min.
• the melt strength (MS) was measured (in cN) with a Goettfert Rheograph 20 (capillary rheometer) in combination with a Goettfert Rheotens 71.97, according to the manufacturer's instructions using the following configuration and settings:
• Barrel chamber and piston diameter 15 mm
• Piston speed 0.32 mm/s, corresponding to a shear rate of 72 s ⁇ 1
• the molecular weights of the LDPE samples were determined with High Temperature Size Exclusion Chromatography (HT-SEC) at 150° C.
• HT-SEC High Temperature Size Exclusion Chromatography
• the molecular weights of the samples i.e. the number-average (Mn), weight-average (Mw), and z-average (Mz) molecular weights, were calculated from Light Scattering (LS) detection.
• Table 4 presents the results obtained for the different LDPE materials, peroxides, and temperature profiles.
• the virgin LDPE's used had almost the same starting MFI (range 19-22) and mainly differed in their terminal vinyl content. Since each polyethylene application requires a specific MFI, it is important to reach similar MFIs after extrusion. In order to achieve this, different amounts of peroxide were required for each LDPE grade. LDPE with low vinyl content required higher amounts of peroxide.
• Table 4 shows that the reactive extrusion of a polyethylene with a low terminal vinyl content leads to melt strength values higher than that of autoclave LDPE, whereas reactive extrusion of polyethylene with high terminal vinyl content gave lower melt strength values.
• the polyethylene obtained by the process of the present invention showed gel formation in cast film close to, or only a little higher, than that of the virgin material and of the same LDPE extruded without peroxide.
• this is shown for gel-particles >600 ⁇ m (which are the most critical particles for, e.g., extrusion coating), but the same effect was seen for smaller gel particles.
• Example 1 was repeated, except for (i) the nature of the LDPE's that were used and (ii) the screw configuration of the extruder.
• the screw configuration used in the present example had three kneading sections—at zones 2-3, 4-5 and 7-8—with no reverse elements at the end of said kneading sections, thereby giving less torque during extrusion.
• the T-profiles used were 180° C. and 200° C. (see Table 3).
• Table 7 presents the results obtained for the different LDPE materials, peroxides, and temperature profiles.
• Trigonox 29 modified 0.15% 200 90 52 7.8 11.7-12.2
• Table 7 shows that the reactive extrusion of LDPE with a low terminal vinyl content leads to melt strength values higher than that of autoclave LDPE, whereas reactive extrusion of LDPE with high terminal vinyl content gave lower melt strength values.
• the gel content of LDPE having a low terminal vinyl content and modified according to the present invention was only a little higher than that of the same LDPE extruded without peroxide ('blank extruded').
• this is shown for gel-particles >600 ⁇ m (which are the most critical particles for, e.g., extrusion coating), but the same effect was seen for smaller gel particles.
• LDPE-B extruded without peroxide at 180° C. had a higher gel-count than LDPE-B extruded at 200° C. This might be due to its higher melt viscosity at 180° C., resulting in higher shear and more LDPE deterioration than at higher temperature.
• LDPE-E and LDPE-C had the same M n , but M w and M z of LDPE-E was significantly higher than of LDPE-C.
• LDPE-E required much more peroxide (0.15% vs. 0.105% Trigonox® 117) to reach MFI 8. Nevertheless, it showed a much lower gel-count, which must be due to its lower terminal vinyl content.

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• 2018
  • 2018-11-23 WO PCT/EP2018/082319 patent/WO2019105851A1/en unknown
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